Method and apparatus for support of sheet material

ABSTRACT

Sheet material, e.g., strip, is supported from above in substantially horizontal position by panels provided with a first plurality of apertures connecting to a source of suction to maintain a sub-ambient pressure between the sheet and panel over a central area of the upper surface of the sheet and a second plurality of apertures connecting to a source of pressure to maintain a supra-ambient pressure over a surrounding peripheral area of the upper surface of the sheet.

United States Patent [1 1 F ournier Feb. 18, 1975 METHOD AND APPARATUS FOR SUPPORT OF SHEET MATERIAL [75] Inventor: Yves Fournier, Chalon Sur Saone,

France [73] Assignee: Saint-Cobain Industries, Neuilly sur Seine, France [22] Filed: Feb. 6, 1973 21 Appl. No.: 330,103

[30] Foreign Application Priority Data Feb. 10, 1972 France 72.04433 [52] U.S. Cl. 248/363 [51] Int. Cl. F16m 13/00 ['58] Field of Search 248/362, 363; 51/235;

[56] References Cited UNITED STATES PATENTS 2,781,554 2/1957 Robinson 51/235 UX 11/1965 Rabinow 248/363 x 8/1966 Hobrough et al 248/362 X FOREIGN PATENTS OR APPLICATIONS 1,400,501 4/1965 France 248/363 Primary ExaminerWilliam H. Schultz Attorney, Agent, or Firm-Pennie & Edmonds [57] ABSTRACT Sheet material, e.g., strip, is supported from above in substantially horizontal position by panels provided with a first plurality of apertures connecting to a source of suction to maintain a sub-ambient pressure between the sheet and panel over a central area of the upper surface of the sheet and a second plurality of apertures connecting to a source of pressure to maintain a supra-ambient pressure over a surrounding peripheral area of the upper surface of the sheet.

4 Claims, 6 Drawing Figures 3,866,875 SHEET 3 BF 3 PATENTED FEB I 8 I975 Q iQ Q a METHOD AND APPARATUS FOR SUPPORT OF SHEET MATERIAL The present invention pertains to gaseous support of material in strip or sheet form, optionally flexible, and particularly to the gaseous support of thermoplastic materials such as glass. It is an object of the invention to provide a method and apparatus for the generation of gaseous cushions or bearings for such support. While in general any gas may be used in the invention, reference will hereinafter for brevity be made to air only.

It is often desirable to grasp a sheet by engagement exclusively with the upper surface thereof so as to be able to transport the sheet into a suitably defined position with reference to a tool or work station. This has been done with suction cups, but they require that the sheets have substantial rigidity, and entail a risk of marring or otherwise damaging the upper surface of the sheets. It is desirable, and in accordance with the invention it is possible, to support the sheets without any element of structure other than air (or other gas) in contact with the upper surface of the sheet. In this way, all marking or abrasion of the sheet is avoided, and it is also possible consistent with the invention to effect movement of the sheet, while so supported, with reference to a fixed working station for example.

It is thus possible not only to transport the sheet from one work station to another but to have access to the lower face thereof for the performance of work operations thereon. The use of air cushions for this purpose has however not been fully developed because of the difficulty in constructing the apparatus and in obtaining stable operation thereof.

The general principle of operation of air cushions for the support of plastic sheets by provision of supraatmospheric pressure from below is well known. Such apparatus maintains, between itself and the sheet, a plurality of layers of air divided into substantially independent zones which are in dynamic equilibrium be tween supply ports on the one hand having a specified configuration or cross section and fed with air at constant pressure, and exhaust ports or openings constituted by open passages between the sheet beingsupported and the apparatus beneath it. The air is thus evacuated laterally, or in spaces between the supply ports.

Given a correct computation of the operating parameters, each portion of the area of a sheet of given thickness is thus held in a stable equilibrium, so long as it is located close to the apparatus. This is an equilibrium between the weight of the sheet, the automatically adjusting pressure of the air cushion, and the counter pressure on the side of the sheet away from the apparatus which maintains the air cushion, e.g., the upper side of the sheet when the air cushion is below it. This counter pressure can itself be obtained with the help of a second air cushion, but it is more usually the pressure of the atmosphere, or of an enclosed space within which a specified pressure is maintained.

When instead a sheet is to be supported by maintenance of sub-ambient or sub-atmospheric pressure above it, the lower face of the sheet is exposed to a fixed counter pressure, usually of the order of magnitude of atmospheric pressure. Hence, the air cushion above the sheet must be below this counter pressure. Considering the most general case of a sub-ambient pressure air cushion according to which the air moves through an open circuit, this requirement of a pressure differential implies that the outlet path from the air cushion must be connected to a suction conduit in which is maintained a pressure below atmospheric. The inlet to the air cushion may however be open to the atmosphere. Otherwise stated, at least one of the blowers which furnishes energy to the apparatus must be located downstream of the air cushion, in the outlet conduit therefrom.

Under these circumstances, it is clear that the various outlet ports from the air cushion must connect to the source of vacuum through passages or conduits along which substantial pressure changes occur as the result of resistance to air flow therethrough. Otherwise, the inadvertent connection of any one of these outlet ports directly to atmosphere would break the vacuum in the entire apparatus.

A device for producing a suction or negative pressure type air cushion therefore comprises essentially a plurality of outlet ports for exhausting air from the region of interest, connected through conduits of suitable flow resistance to a source of negative pressure.

It is an object of the present invention to provide a suction type air cushion device whose operation is highly dependable even though the apparatus itself is particularly simple.

According to the invention, in order to avoid that a local loss of support for the sheet at its edge .or at a corn'er or other discontinuity of the apparatus should result in a cumulative loss of support and fall of the sheet, the supporting regions of the cushion operated at subatmospheric pressure are surrounded by a stabilizing belt at supra-atmospheric pressure, or in any event at a pressure higher than the ambient one. To this end, the inlet openings, for supply of air to the air cushion, and in particular those supplying air at the peripheral regions of the cushion, receive air at supra-ambient pressure.

With this construction, a loss of support of the sheet at a local position adjacent the edge of the sheet produces initially or incipiently a decline in pressure above the sheet at that locality. This tends to correct the failure rather than to contribute to a cumulative loss of support for the sheet.

It is of course not necessaryv that the supporting zones of suction (where air is exhausted from the air cushion) be surrounded by a complete belt or ring of inlet ports supplied with air at supra-atmospheric pressure, provided only that the spacing or separation of such inlet ports be small enough so that incipient fall of the sheet at any portion of its edge shall produce the automatic compensatory action which has been described.

In one preferred embodiment, the apparatus of the invention comprises at least one panel disposed crosswise of the direction of motion of the sheet (in the case of a moving strip to be supported). lnlet and exhaust ports open onto the smooth lower surface of the panel, below which the strip or sheet is to be supported, with the inlet openings, supplied with air at supraatmospheric pressure, occupying generally a peripheral area of the panel surrounding a central area occupied by the exhaust ports at which a sub-ambient pressure is maintained.

Plural such panels may be disposed side by side in suitable number so as to constitute a surface which may be either plane, or of desired curvature with the purpose of making it possible for the sheet to be shifted in level.

The ports may be disposed in rows, the rows being grouped in pairs with each inlet row corresponding to an exhaust row. It is further possible to dispose the ports in diagonal fashion with respect to each other for the purpose of avoiding all risk of marking of the sheet, either on start-up or during operation.

The panel or panels may comprise two groups each of two rows of complementary inlet and exhaust ports, the rows extending transversely of the direction of mo tion of the sheets or strip. These rows of ports may be rectilinear and may be disposed transversely or at right angles to that direction.

According to one advantageous feature of the inven tion, each of these inlet and outlet ports is formed as a slot left between a borein the panel and a stopper inserted in the bore and incompletely closing it. The bore may include a counterbore at the exposed surface of the panel. The stopper may have a longitudinal slot or fiat along its length so as not to fill the bore, and it may have a head with a flat incompletely filling the counterbore.

In this way there may be provided a narrow channel which opens via a zig-zag or labyrinth into a chamber of larger section which is disposed on the side of the head of the stopper. It is convenient to provide this channel by machining flats on the stopper. The inlet and exhaust ports thus take, at the exposed surface of the panel, the form of circular segments, preferably disposed with their limiting chords in a direction essentially parallel to that of the rows of ports and therefore perpendicular to the sense of motion of the sheet. Differences of temperature, either imposed or accidental, may exist between the sheet and the circulating air of the cushion. In order to improve distribution of the air currents so as to improve regularity in the thermal effects, the ports, i.e., the segments, may be inclined to this direction by an angle which is below 30 and is preferably between and The stoppers which help to define the inlet and exhaust ports may be flush with the surface of the panel or they may lie above that surface, i.e., be farther than that surface from the sheets being supported. Advantageously the inlet and outlet ports may be formed with stoppers having similar heads, but the exhaust ports are of greater cross section so as to present a smaller resistance to the flow of air. The ratio of the two cross sections may be of the order of two.

The invention will now be further described in terms of a presently preferred embodiment thereof and with reference to the accompanied drawings in which: I

FIG. 1 is a vertical section taken on the line I-I in FIG. 4 through a panel in accordance with the invention and through a sheet supported by it;

FIG. 2 is a diagram showing air pressure in the space between the panel and sheet of FIG. 1 as a function of position crosswise of the panel;

FIG. 3 is a view in perspective of the panel sectioned along the line IIIIII of FIG. 4;

FIG. 4 is a plan view of the panel from beneath, showing a presently preferred distribution of inlet and outlet ports and showing how a plurality of panels may be associated together;

FIG. 5 is a sectional view at an enlarged scale of one of the ports, showing how the port is defined between an aperture in the panel and a stopper partly closing the aperture; and

FIG. 6 is a perspective view of the stopper of FIG. 5.

In the embodiment illustrated, the invention includes a plate 1 whose lower face 2 adjacent the sheets 3 to be supported is smooth. The plate includes rows of exhaust ports or openings 4 and inlet ports or openings 5 for passage of a gas, which may be air, to provide the gaseous cushion for support of the sheet 3.

The plate 1 is fixed to a body 7 in which are provided chambers or manifolds 8 and 9. Center chamber 8, communicating with ports 4 over a central area of plate 1, connects by a conduit or conduits 10 with a source of suction, schematically indicated as a pump 6. Lateral chambers 9, communicating with ports 5 over a periph eral area of the plate generally surrounding the area occupied by ports 4, connect with the high pressure side of pump 6, which may be a blower. The plate 1, with its stoppers 15 presently to be described, and the member 7, make up a panel according to the invention, generally indicated at reference character 24. A number of such panels may be combined, as seen in FIG. 4. In FIG. 1 the sheet may move from left to right or from right to left.

FIG. 2 indicates schematically, for the space between the plate 1 and the sheet 3 of FIG. I, the variation in pressure with position crosswise of the panel. In FIG. 2, pressure is plotted vertically and crosswise position horizontally, zero pressure signifying the ambient or atmospheric pressure. The average pressure is seen to be below ambient. At the edge of the panel, the pressure is atmospheric. It rises to a supra-atmospheric maximum at the inletor supply ports 5, and declines to a minimum, below atmospheric, opposite the exhaust ports 4. I

As indicated in detail in FIGS. 5 and 6, the plate 1 includes for the ports 4 and 5 cylindrical openings or bores 13 which extend from the chambers 8 and 9 down to counterbores 14 of larger. diameter. These counterbores constitute chambers open to the working face 2 of the panel. The stoppers 15 are disposed in passages defined by the bores and counterbores. Each stopper has a stem 15' and a head 12 disposed respectively in one of the bores 13 and counterbores l4. Flats l6 and 17 are formed on the stem and head, joined at a fillet 18 which constitutes a plane surface perpendicular to those flats and which leaves a free space between the stopper and the wall 19, which latter constitutes the bottom of the counterbore.

The space 20 between the flat l6 and the bore 13, the space 22 between the fillet 18 and the bottom 19 of the counterbore, and the space 21 between the flat l7 and the counterbore thus form together a port or passage of zig-zag or slightly labyrinthine shape.

It will be observed that the cross section of the pas sage is larger at 21 and at 22 than at 20 so as to hold down the streaming velocity of the air at the surface of plate 1. This makes it possible to reduce heat exchanges with the sheet 3.

On the stoppers of the exhaust ports 4 the flats 16 are wider than on the stoppers of the inlet ports 5, so that the passages 20 are of greater flow cross section in the exhaust than in the inlet ports. The pressure change in the exhaust ports 4 between the chamber 8 and the surface 2 of the plate 1 may be as little as one-fifth of the pressure change in the inlet ports 5 between the chambers 9 and the surface 2.

The stoppers may include at the upper end of their stem a bevelled portion 23.

As indicated in FIG. 4 it is possible to provide a succession of panels in a desired number according to the separation of the locations between which the sheets are to be moved, these panels being supported parallel to each other and transversely of the direction of motion of the sheets. The means for moving the sheets may be conventional and are not shown. The panels may be inclined with respect to each other so as to follow a curvature on the path of motion when the sheets are to be moved for example between locations of different height. As indicated in the drawings, the inlet and exhaust ports may be disposed diagonally with respect to each other.

It is to be understood that the invention is not limited to the embodiment described but rather may comprehend many variations thereonand departures therefrom. It is also clear that the apparatus described may readily serve for a supra-atmospheric gas cushion operating on the lower surface on the sheet, in which case the exhaust conduit 10 may be open to the free atmosphere.

I claim:

I. Apparatus for the support of sheet material from above against the force of gravity, said apparatus comprising a plate having a plurality of exhaust ports there through for the aspirated exhaust of gas from beneath said plate and having a plurality of inlet ports therethrough for supply of gas through the plate to the space below it, said inlet ports being disposed at least in part on opposite sides of said exhaust ports, a stopper partly obturating each of said ports, the stoppers in the inlet ports being of a different size from those in the outlet ports means to maintain a sub-ambient pressure at said exhaust ports and means to maintain a supra-ambient pressure at said inlet ports.

2. Apparatus according to claim 1 wherein said apertures comprise a bore and counterbore and wherein said stoppers comprise a stem and a head respectively partially filling said bore and counterbore.

3. Apparatus according to claim 2 wherein said stoppers are formed with flats on the stem and head thereof whereby said apertures are of substantially circular segmental cross section.

4. Apparatus according to claim 3 wherein the chords limiting said segments are inclined at an angle between 0 and 30 to the direction perpendicular to the direction of motion of said material. 

1. Apparatus for the support of sheet material from above against the force of gravity, said apparatus comprising a plate having a plurality of exhaust ports therethroUgh for the aspirated exhaust of gas from beneath said plate and having a plurality of inlet ports therethrough for supply of gas through the plate to the space below it, said inlet ports being disposed at least in part on opposite sides of said exhaust ports, a stopper partly obturating each of said ports, the stoppers in the inlet ports being of a different size from those in the outlet ports means to maintain a sub-ambient pressure at said exhaust ports and means to maintain a supra-ambient pressure at said inlet ports.
 2. Apparatus according to claim 1 wherein said apertures comprise a bore and counterbore and wherein said stoppers comprise a stem and a head respectively partially filling said bore and counterbore.
 3. Apparatus according to claim 2 wherein said stoppers are formed with flats on the stem and head thereof whereby said apertures are of substantially circular segmental cross section.
 4. Apparatus according to claim 3 wherein the chords limiting said segments are inclined at an angle between 0* and 30* to the direction perpendicular to the direction of motion of said material. 